(1) Field of the Invention
This invention relates to a surveying apparatus capable of making a route survey in road building, tunneling work and so on with remarkable accuracy, and particularly to a surveying apparatus in which a laser spot formed by irradiating a laser beam on a target is analyzed as to its coordinate deviation to determine the curvature of a route or the like.
(2) Description of the Related Art
Traverse surveying which has been conventionally adopted in road building, tunneling work and so on has been significantly improved with respect to measuring accuracy and feasibility due to electronics. Among conventional electronic surveying methods, a laser surveying method has advantageously been applied to actual fieldwork in constructing a road, a tunnel and so on. In this laser surveying method, a coherent laser beam irradiated from a laser oscillator impinges a target spaced from the laser oscillator to form a laser spot on the target and a positional deviation of the laser spot on the target is arithmetically calculated by a computer so as to measure the curvature and/or orientation of a route to be surveyed, whereby a route survey can be carried out with considerable accuracy. Examples of conventional surveying apparatuses of this type are described in British Pat. No. 2,143,396(B) and Japanese Patent Application Public Disclosures SHO 56(1981)-104209(A), SHO 57(1982)-63415(A), and SHO 57(1982)-96213(A).
These prior art apparatuses adopt a structure in which the laser oscillator and the target are separated from each other. With such a structure, therefore, it is difficult to determine the orientation and position of the taget relative to the origin position at which the laser oscillator is located.
The inventor of the present invention formerly proposed a surveying apparatus in Japanese Patent Application Public Disclosure SHO 60(1985)-243508(A), in order to eliminate the aforementioned drawback suffered by the conventional surveying apparatus in which the laser oscillator and the target are separated.
The proposed surveying apparatus has a structure in which a main cylinder incorporating a laser oscillator is bendably connected with a guide cylinder incorporating a target on which a laser beam from the laser oscillator impinges to form a laser spot. This proposed apparatus is easy to handle and uses a simple arithmetic operation for analyzing the coordinates of the laser spot on the target, because the distance between the laser oscillator and the target is fixed.
In the proposed apparatus, however, a joint for bendably connecting the main cylinder incorporating the laser oscillator with the guide cylinder incorporating the target is formed by a sealing member comprising elastic material such as rubber. Therefore, the range within which the guide cylinder is allowed to bend is narrow so that a route having large curvature cannot be surveyed. Besides, the elastic material undergoes a secular change, and therefore, the joint is of poor lasting quality and there is a possibility of the distance between the laser oscillator and the target varying elastically.
Furthermore, it can by no means be said that it is desirable to locate the joint for bendably connecting the main and guide cylinders with each other in the vicinity of the laser oscillator as done in the aforementioned surveying apparatus formerly proposed by the inventor of the present invention. That is to say, because the measuring accuracy of the surveying apparatus of this type depends on not only the resolving power of an image pickup means for detecting a laser spot formed on the target but also on the amount of the positional deviation of the laser spot on the target, it seems that the measuring accuracy can be improved by disposing the joint between the main and guide cylinders in the vicinity of the laser oscillator so as to enlarge the positional deviation of the laser spot. However, the structure in which the joint is disposed near the laser oscillator can in no way bring about a relatively large deviation of the laser spot from the center of the target.